Ebola Characteristics and Comparisons to Other Infectious Diseases
The current outbreak of Ebola virus in West Africa has been declared a public health emergency of international concern by the World Health Organization (WHO) and is the most severe such outbreak of Ebola to date. Almost eight in ten cases ever reported have been reported in the past few months alone, and there is increasing attention to and concern about its further escalation.
Ebola virus has a unique set of characteristics that determines how and why it spreads, and how deadly it can be. To better understand it, we compare Ebola to 12 other infectious diseases that continue to represent public health challenges today. These include diseases that have been around for thousands of years (the so-called “ancient diseases”) as well as others that are much more recent (the so-called “emerging diseases”). They include viruses as well as bacteria and parasites, and vary in terms of how easily they are spread, how deadly they are, and whether there are vaccines, treatments, or cures to address them.
1. How is Ebola transmitted?
How an infectious disease is transmitted – whether through direct contact with bodily fluids, through air, or other means, as well as whether human-to-human transmission is possible – is important for understanding how to prevent and track the disease. Ebola is transmitted only through direct contact with bodily fluids, as are HIV and Hepatitis C. Other diseases, such as measles and SARS, are transmitted through airborne means. Human- to-human transmission occurs for all of the diseases included in this profile except for malaria, which is transmitted by mosquitoes to humans.
2. Is asymptomatic transmission of Ebola possible?
Some diseases can be transmitted only when symptoms are present while others can be transmitted even when a person does not yet have symptoms, known as being asymptomatic. Ebola can only be transmitted when symptoms are present, in contrast to diseases such as HIV, influenza, and malaria which have asymptomatic transmission.
3. How long is Ebola’s incubation period?
The incubation period of a disease is the time between initial infection and when symptoms first appear. Ebola’s incubation period of 2 to 21 days is fairly short compared to other infectious diseases such as HIV, which can have an incubation period of 10 years or even longer. It is also shorter than the incubation period for Tuberculosis and Hepatitis C. However, some other infectious diseases, such as SARS and influenza, have, on average, shorter incubation periods than Ebola.
4. Is there a vaccine, treatment, or cure for Ebola?
Currently, there is no vaccine to prevent Ebola, no treatment for the disease (other than treatments for its symptoms and some experimental treatments), and no cure. Other diseases have treatments but no vaccine and no cure (such as HIV), while still others have vaccines, but cannot be treated or cured (such as measles).
5. How deadly is Ebola?
Ebola is one of the most deadly infectious diseases, causing death in approximately 50-90 percent of those who become infected (its estimated case-fatality rate). This is much higher than almost every other infectious disease included. Case fatality rates for other diseases are much lower, including those for influenza (less than 1%) and SARS (13-43%).